2. Field of the Invention
This invention relates to novel, lower alkyl ester derivatives of aromatic sulfonic acids of surfactant character and the preparation of lower alkyl esters of alkylated aromatic and aliphatic sulfonic acids. A subclass of these compounds, which is of particular interest, consists of alkylated benzene sulfonic acid methyl esters. Another aspect of the invention is concerned with the preparation of the sulfonate esters of the present invention via the alkylation of the corresponding sulfonate salts with dialkyl sulfates, particularly dimethyl sulfate. A further feature of this aspect is the isolation of the novel sulfonate esters by extraction, distillation and crystallization.
2. Description of the Prior Art
Lower alkyl esters of aliphatic, aromatic and alkyl substituted aromatic sulfonic acids are described in the art. For example, information relating to the aforesaid compositions is disclosed in U.S. Pat. No. 2,017,803; British Pat. No. 669,592; U.S. Pat. Nos. 3,206,492; 2,831,013; 3,818,102; 3,853,939; 3,882,238; 3,301,886; French Pat. No. 987,054 (abstract in Chemical Abstracts Volume 50, column 7139); U.S. Pat. No. 2,613,195; "Surface Active Agents and Detergents" Volume 2, page 87, Schwartz et al, Interscience Publishers (1958); French Pat. No. 940,088 (abstracted in Chemical Abstracts Volume 1950, column 7353); British Pat. No. 673,842 (abstracted in Chemical Abstracts Volume 46, column 11724); Japanese Pat. No. 73 40, 737 (abstracted in Chemical Abstracts Volume 8179678f); British Pat. No. 673,842; and British Journal of Industrial Medicine, Vol. 10, pp. 121-124 (1954).
J. S. Showell, J. R. Russell and D. Swern described the synthesis of C.sub.12 to C.sub.18 alkane sulfonic acid methyl ester by reacting the corresponding acids with diazomethane. For reference, see J. Org. Chem. Vol. 27, pages 2853 to 2858, 1962. A. Nersarian and P. R. Johnson prepared the C.sub.1 to C.sub.4 alkyl esters of dodecane sulfonic acid and the methyl ester of chlorosulfonated polyethylenes from the corresponding sulfonic acid silver salts and alkyl iodides according to W. D. Emmons and A. F. Ferris. See J. Appl. Polymer Sci., Vol. 9, pages 1653 to 1668, 1965 and J. Am. Chem. Soc., Vol. 75, page 2257, 1978. Straus et al in U.S. Pat. No. 3,875,102 discloses the synthesis of the methyl esters of oligomers of detergent sulfonic acids by reacting the oligomeric acids with diazomethane.
The synthesis of lower alkyl, particularly methyl esters of sulfonic acids is a much studied reaction. Metzger et al in U.S. Pat. No. 3,301,886 (cited above) disclose the synthesis of lower alkyl esters of aromatic sulfonic acids, including esters of i-dodecylbenzene sulfonic acid, by reacting metal salts of the corresponding acids with dialkyl sulfates in the presence of a base, preferably sodium bicarbonate. The preparation of such esters from the corresponding sulfonic acid sodium salts via alkylation with dimethyl sulfate generally at temperatures above 150.degree. C. was studied by several workers: F. Ullmann, Ann. der Chemie, 327, 117 (1903); A. Werner, ibid. 321, 269 (1902); P. Ruggli and E. Peyer, Helv. Chim. Acta 9, 939, 946, 948 (1926); H. J. Barber et al, J. Appl. Chem. (London) 3, 253-265 (1953). Free sulfonic acids could be methylated at about 80.degree. using a highly reactive derivative of dimethyl sulfate and dimethyl formamide as disclosed by C. W. Schroeck in U.S. Pat. No. 3,956,354. The same patent also discloses a similar reaction of sulfonic acids with triethyl phosphate.
Another frequently used method, applicable to the synthesis of aromatic sulfonic acid esters, employs the reaction of the corresponding aromatic hydrocarbons with methyl or ethyl chlorosulfonate: F. W. Bushong, Am. Chem. J. 30, 212-224 (1930); M. Frerejacque, Ann. der Chimie, 14 (10) 147-226 (1930); and the above cited article by Cruikshank et al. Finally, the reaction of the corresponding sulfonic acid chlorides with alcohols in the presence of acid binding agents is also generally applicable for the synthesis of the prior art compositions: W. Rodionow, Bull. Soc. Chim. 39 (4), 305-325 (1926); V. C. Sekera and C. S. Marvel, J. Am. Chem. Soc. 55, 345-349 (1933); B. L. Emling, ibid. 74, 4703-4704 (1952). The esters of 4-toluene sulfonic acid were studied as plasticizers for nitrocellulose lacquers by A. Kraus, Arbeitsgemeinschaft Farben and Lacke, Nos. 5 and 6, 27-28 (1943).